Determination of water droplet size distribution in butter: Pulsed field gradient NMR in comparison with confocal scanning laser microscopy

The size of the water droplets in butter determines its microbial stability and sensorial properties. In this work, two techniques to determine the water droplet size distribution in butter were compared, namely confocal scanning laser microscopy (CSLM) and pulsed field gradient nuclear magnetic resonance (pfg-NMR). Six commercial butters from different manufacturers were studied. CSLM proved to be a good method to obtain visual information on the microstructure of the butter, but its limited resolution makes it less suitable for the accurate determination of droplet size distributions containing an important fraction of submicron particles. pfg-NMR gives no visual information, but sample preparation, measurement and data analysis are less time consuming. This method yields reproducible quantitative information. However, the accuracy depends on the correctness of the assumptions made. For all samples, except the one containing the biggest droplets, significantly different results were obtained by both techniques.